After a well has been drilled to produce oil or gas and the well is placed in service, it is normally necessary to provide periodic maintenance or service to the well. This is often carried out by use of a device commonly known as a workover rig. A typical workover rig sometimes is too large for routine or small maintenance jobs which may only require one or two days to execute. To place things in perspective, a typical drilling rig is sufficiently tall to hold three joints of pipe which are about 90 to 93 feet in length. Accordingly, the drilling rig is taller, measuring from the rig floor to the crown block. It is not uncommon for drilling rigs to be 130 feet in height. A workover rig is typically tall enough to handle production tubing above the rig floor. If the tubing is provided in 30 foot lengths, and the workover rig is intended to be on site for several days, a large workover rig is sufficiently tall enough to pull and stand two joints of tubing, perhaps even three joints. However, most workover rigs are relatively short and handle a single joint of tubing is permitted to stand in the rig. This requires a rig standing perhaps 40 to 45 feet in height. When rigs are this small, they typically can be constructed on the back of a truck, pivotally mounted so that they can stand upright when required, and folded horizontally to enable the truck to travel the highways. This defines a truck which is sufficiently low when the rig is folded down that it can travel down the highway within the length restrictions permitted for the truck. Regrettably, a truck mounted workover rig is not always available for every location.
There are many locations which cannot be reached by a long workover rig traveling down the highway on a truck. As an example, there are rig locations in swamps or remote areas where there are not adequate rural roads available to get to the site of the well that requires servicing. There are wells located in offshore waters where the well connects to a small platform located in a few feet of water. In many shallow regions, it is not uncommon to build a single platform for the well. This of course is to be distinguyshed from the large platforms erected miles out into the Gulf of Mexico to a locate as many as 30 or 40 wells drilled from a single platform utilizing deviated welled drilling techniques to extend the wells from such a platform into the producing formations.
The present disclosure describes a structure which can be used for workover. It is a structure which does not require a long truck traveling down the highway. Rather, it is a structure which can be mounted on a much smaller pallet for truck transportation to and from remote well sites. It provides a package which can be mounted on a relatively small skid moved by a boat, barge and even by helicopter to remote sites. It is a package which assembles and disassembles so that it can be erected on site, thus providing a small package for easy transportation to and from the remote location. The present disclosure is particularly advantageous in that it sets out a workover rig which can be erected at the site of a workover job and can be used to handle relatively long tools. If the tool to be placed in the well during workover is relatively short, a modest gin pole can be erected above the well head. However, there are difficulties in accomplishing this. For one, the well normally is operated at an elevated pressure, the pressure being as much as several thousand psi above atmospheric pressure. This of course depends on the particular formations that have been drilled and the pressure which is observed in the well at the well head equipment. Where there is substantial pressure in the well, it is necessary to use a device known as a lubricator or stuffing box to enable the operators at the surface to insert tools into the well. Where there is almost no pressure differential, the lubricator or stuffing box is relatively short. Whether the stuffing box is long or short, it is first affixed to the well head equipment to enable entry at the top end of the stuffing box. In that case, the lubricator positions the point of insertion of the service tools or equipment well above the platform, deck or other working area adjacent to the well head equipment. That requires a gin pole of substantial length, typically sufficiently tall that a gin pole simply will not do. Even more difficult than that, the length of the tool to be inserted through the stuffing box is a material factor. If for instance the well head equipment stands five feet above the working platform at the well head, and a stuffing box must be attached to it which adds another feet in length, immediately difficulties arise for the personnel getting to the point of entry of the tools to be inserted into the well. If the service equipment is quite long, 20 or even 30 feet for some tools, then the service personnel are required to insert an extremely long tool into the opening of the stuffing box at a height well above the working area.
The present apparatus is able to accomodate such heights. Indeed, it is a system which can be assembled from parts used repetitively at the site of the well and can be constructed to heights. In one job, this equipment can be used to provide an overhead structure which stands 30 feet tall. At the next job it can be extended to 60 feet, and at the next job it can be extended to 90 feet, just citing three representative heights. The equipment of this disclosure can be rigged up in relatively short order. Moreover, it is equipment which is rigged up so that it can be assembled to the selected height, used for a few hours, disassembled and then stored on a pallet or skid, hauled by truck or barge as mentioned, thereby enabling the next job to be carried out.
One of the advantages of the present apparatus is that the height of the tower can be extended without load loss. There are some service tools which impose a line load limit on the equipment. Assume for instance that a 500 pound tool is to be lowered into a well for operation. Assume further that the maximum pull which can be applied to the line in the well is limited to 1,000 pounds, or a total of 1,500 pounds of load. This load must be handled by a line which extends through the well, through the well head equipment, through the stuffing box and over the temporary derrick which is provided by the present disclosure. That load is derrick. The line loads the derrick from the winch typically located up the derrick and then over a sheave at the top of the derrick and down into the well. As the derrick is extended to greater heights, there is a requirement for guy wires to be tied to the derrick. If the guy wires are anchored at the top of the derrick, and if they are pulled with substantial tension, this adds compressive loading to the derrick and decreases the load that can be carried by the derrick from the load line. The present apparatus incorporates a system whereby the load on the derrick by the means of guy wires to maintain the derrick vertically, to resist wind gusts, and overcome other dangers, is partly placed on an upstanding part of the structure which is not part of the derrick. As will be explained in detail below, this type of guy system ties a set of guy wires to an upstanding member which aligns the derrick sections. The downward pull of the guy wires on this member can be quite high but this load is not added to the derrick load. The derrick merely rests within it, but alignment is accomplished it so that the derrick is free of loading from the guy wires which assure vertical alignment. An additional set of guy wires can then be tied to the derrick from the top to extend outwardly, but the downward load on this set of guy wires is held to a minimum. This set of guy wires assures that the top is positioned above the bottom of the derrick for vertical alignment. Nevertheless, extreme loads are placed elsewhere, not on the derrick.
One of the advantages of the present apparatus is that it enables the system to be assembled without requiring climbing to the top of the derrick to do this. The personnel who assemble the derrick can assemble a tall derrick, for instance, one that is 60 feet tall without having to climb to the top of the derrick. It is assembled section by section from the bottom. Accordingly, this requires that the personnel climb only about 12 to 15 feet. An appropriate catwalk is provided at the necessary height. Personnel safety is markedly enhanced. Each section of the derrick that is added is then added at the bottom. As each section is added, the derrick is extended but the personnel involved in the assembly are not required to go any higher than the catwalk. Rather, they can remain at this low elevation. When their work is accomplished, they can then dismount the catwalk and carry out the well service procedures without having to climb to the top of the derrick.
The present apparatus is summarized as a derrick incorporating an integral construction mechanism which permits erection of the derrick structure section by section. First, a base is installed. The base constructed so that it has appropriate degrees of freedom which permit pivoting, there being two axes of rotation at right angles so that leveling is obtained for the rectangular structure at the base. It is leveled, ideally using a bubble level, thereby assuring that the derrick will be erected with a true vertical angle. The base, after assembly and installation on a level reference, then supports an upstanding heavy frame structure of significant height denoted herein below as the launcher. So to speak, it is a guyde mechanism which is anchored to the base and is then tied with a number of guy wires. The several guy wires connected to the launcher can be pulled extremely tight to assure that the launcher is well anchored in position. Compressive loading in the launcher can be quite high but that does not impart any loading whatsoever to the derrick. Rather, the launcher is provided with a door which permits section by section insertion of the derrick into the launcher. The launcher additionally incorporates a mechanism which reaches down into the launcher to lift and hold a section of the derrick. The launcher incorporates a lift mechanism of limited travel which raises the sections of the derrick. As the first and then the second and then the last sections are inserted, each being assembled from the bottom, the launcher then extend the partially completed derrick upwardly from the bottom. Each section that is added into the launcher is vertically aligned by the launcher. Sections are joined together with quick release mechanisms to enable easy assembly in the field. There is a turn table which is affixed to the top derrick section. That turn table supports appropriate sheaves as will be described which enable the load lines to be correctly routed from the ground located winches which operate the load lines. As the sections are added to the derrick and as its length is extended so it becomes taller, it is raised above the launcher. Every connection required at the launcher is made complete so that the personnel need not climb up the derrick during assembly of the derrick. Likewise, at the time of disassembly, the derrick is taken apart from the bottom and the sections are removed from the launcher for easy storage. The entire derrick is disassembled and stored without requiring climbing above the launcher. The launcher itself supports a small overhead gin pole to enable each section to be handled while on the exterior of the launcher, and there is additionally a hoist mechanism on the interior of the launcher. That is used for raising the partially assembled derrick aligned with the launcher. In addition, the launcher supports foldable catwalk or deck members at the top end which are relatively low and therefore which do not have the risk involved with great heights. The launcher additionally supports a door which enables latching of the sections of the derrick on the interior of the launcher. The door can be opened and closed as sections are placed in the launcher.